The multistep α-transfer treatment of Aleixo et al. is employed in a detailed investigation of the anomalous back angle scattering of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{28}$Si. We have improved the calculation of the propagator in the transfer channel and taken into account the coupling to elastic transfer. This way, we have obtained a good description of the experimental back scattering cross section from the barrier energy to ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$∼50 MeV. It is shown that the rise of the cross section at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$∼45 MeV can be explained by parity-dependent terms in the S matrix, arising from the coupling to the elastic transfer channel. A study of the conditions for the coupling with an α-transfer channel to produce dynamical Regge poles indicates that pickup channels can be left out.

• Received 23 January 1990

DOI:https://doi.org/10.1103/PhysRevC.42.2628